Virial contraction under stellar evaporation
= Virial contraction under stellar evaporation
{title2=$R_g\propto M^2,\quad\bar\rho\propto M^{-5}$}
For an isolated quasistatic cluster with near-zero escape energies, the bound negative energy is approximately fixed. The <virial theorem> and <gravitational radius> then imply $R_g\propto M^2$. A homologous mean density scales as $M^{-5}$ and increases as mass evaporates. Tidal limitation or finite positive escape energies modifies this simple model.